WO 2006/064495 A1 discloses a method for monitoring heat damage to tissue during a heat ablation procedure. While a certain part of the tissue is ablated, ultrasound images of neighboring parts of the tissue are acquired, and from these ultrasound images a parameter is extracted, which is indicative of a biological response of the neighboring parts of the tissue to heat. In an embodiment, the parameter is the accumulation of bubbles and a damage of the neighboring parts of the tissue is determined based on this parameter. The aim of this monitoring method is the detection of unwanted damages to the neighboring parts of the tissue. The monitoring method monitors therefore a possible damage of the tissue by observing spatial and temporal changes in the ultrasound images and by relating these changes to bubble formation. This monitoring leads to inaccuracies in determining possible damages of the tissue, because bubble formation reflects only high temperature in the tissue, but is not directly linked to the extent of tissue damage.